The present invention relates generally to temperature indicators, and is particularly concerned with apparatus and methods for indicating or monitoring the exhaust gas temperature in gas turbine engines.
In the operation of gas turbine engines, particularly those used as aircraft powerplants, it is important to continually monitor the exhaust gas temperature of the engine during all phases of operation. A rise in the exhaust gas temperature beyond normal limits may be indicative of an abnormality in the operation of the turbine engine, requiring corrective action by the flight crew or maintenance personnel. Moreover, overtemperature conditions (regardless of cause) are of concern in and of themselves, since their number and duration will affect the lifetime of the engine and the frequency with which it must be inspected and maintained. Generally, the manufacturer of a turbine engine specifies different temperature bands or zones in which the engine is permitted to operate for particular amounts of time, as well as the types of inspection and/or maintenance procedures that are required when these limits are reached.
In the past, it has typically been the responsibility of the flight engineer to monitor the exhaust gas temperature of an aircraft turbine engine, and to note any overtemperature conditions for later use in diagnosing engine problems and calculating maintenance intervals. However, this task is among many others that the flight engineer must perform in a complex multi-engine aircraft, and it is entirely possible for brief overtemperature events to be overlooked by the flight engineer when other distractions are present. To compound the problem, many types of turbine-powered aircraft (particularly smaller aircraft and newer aircraft designed for smaller flight crews) do not provide a separate flight engineer station, and hence the task of monitoring exhaust gas temperatures may shift to the pilot or copilot. In these situations, the capability of automatically monitoring the exhaust gas temperature of a turbine engine becomes highly desirable. Various types of automatic monitoring and recording instruments have been proposed to meet this need.
U.S. Pat. No. 4,575,803, issued to M. Samuel Moore on Mar. 11, 1986, discloses a turbine engine monitoring and recording system in which overtemperature levels are segregated according to temperature band, and the accumulated time during which the engine is within each overtemperature band is measured and recorded in a non-volatile memory. The system includes a remote display panel which may be mounted in the cockpit of an aircraft. A switch on the panel may be operated to cause a digital display unit to indicate the length of time beyond the manufacturer's rated time of operation in the temperature band under consideration. The temperature bands are selected for display using a series of pushbuttons, with each pushbutton corresponding to a separate temperature band or channel. Although this system provides an indication of the accumulated time during which the engine has operated in a given overtemperature band, it does not provide information about individual overtemperature events. This is a significant disadvantage, since a sustained overtemperature condition is generally more harmful to a turbine engine than a series of shorter overtemperature excursions, and it is desirable to be able to distinguish one situation from the other. In addition, knowledge of the number and duration of the individual overtemperature events can be helpful in diagnosing specific types of engine problems for which maintenance may be required.
In U.S. Pat. No. 3,946,364, issued to Joseph Codomo et al on Mar. 23, 1976, overtemperature conditions in jet engines are indicated by means of a light-emitting diode matrix which graphically displays each overtemperature incident in the form of a histogram. In one embodiment, a plurality of overtemperature events are stored for later retrieval, and the indicator device is interrogated to cause it to sequentially display each stored overtemperature event. While this system can provide some useful information about individual overtemperature events, the graphical format of the display is inherently limited in the amount and type of information which can be displayed. Thus, for example, critical information regarding the duration and peak temperature of each overtemperature event can be displayed only approximately and within the limits of the scale of the display. This limits the usefulness of the device for monitoring and diagnostic purposes.
U.S. Pat. No. 4,821,216, issued to John S. Howell et al on Apr. 11, 1989, discloses a multi-function aircraft meter for displaying peak engine temperature, length of time over a predetermined temperature, excessive temperature, and peaks over a temperature limit for both engine starting and operation modes. A combined analog and digital display is provided, and a separate warning indicator is also provided to alert the pilot that a predetermined temperature condition has been exceeded. Temperature exceedences in different bands are detected, and an electromagnetic ball relay is actuated to indicate that an exceedence has occurred. Although the instrument is useful for real-time monitoring of turbine exhaust gas temperature, the lack of any recording capability (other than by actuation of the ball relay) means that it is of only limited utility when a detailed history of individual overtemperature excursions is desired for maintenance or diagnostic purposes.